This invention relates to a screen printer (or sometimes called “stencil printer”) in the field of Surface Mount Technology (“SMT”), more particularly but not exclusively, for solder paste printing. This invention also relates to a method of cleaning a stencil (or a screen) of a screen printer.
In SMT, a stencil is normally placed over an electronic device, such as a printed circuit board (PCB) having solder pads on which respective leads of a surface mount component are placed. The stencil includes apertures which correspond to respective solder pads and a solder paste printing process is used to print solder paste on the solder pads. After a few printings, the apertures of the stencil may be partially blocked by residual solder paste and the entire stencil should be cleaned to prevent bridging, mis-printings or defects. For stencils with very small apertures (for example small area-ratio apertures), the apertures may become blocked more easily and it may be useful to clean the stencil after each printing. However, current cleaning methods tend to be relatively inefficient, take an unacceptably long time to clean the stencils and need a lot of cleaning material.